1. Field of the Invention
The present invention relates to a wholly aromatic polyamide fiber having improved surface frictional characteristics.
More particularly, it relates to a wholly aromatic fiber which exhibits a reduced filament-to-filament friction coefficient under a high contact pressure, is almost completely neither broken nor fibrillated at the twisting step, and has excellent fiber qualities such as a high strength of a twisted cord.
2. Description of the Related Art
In order to meet recent demands for increasing the strength and modulus of fibers, various novel fiber-forming materials have been proposed.
However, most of these fibers have a high rigidity and a hard touch, and fibrillation is readily caused by friction among filaments. Consequently, fluffing or filament breaking is readily caused. These defects result in degradation of such characteristics as strength and modulus.
As means for obtaining a fiber having high strength and modulus, a method has been adopted in which drawing is carried out at a high draw ratio under high temperature conditions. In this method, however, fusion bonding is readily caused among individual fibers of a fiber bundle. As means for preventing this fusion bonding among fibers, a method has been proposed in which fine particles of an inorganic substance are applied to an undrawn yarn in advance (see Japanese Unexamined Patent Publication No. 58-54021, No. 53-147811 and No. 54-15020).
However, a fiber to whose surface an inorganic substance has been applied in the form of fine particles or a coating film exhibits increased frictional characteristics. Accordingly, if these fibers are used in the form of twisted yarns, for example, as rubber reinforcement for tires, belts, and hoses, or if several multifilaments are twisted for production of ropes, fishing lines, and the like, the high strength, which is a high-performance characteristic inherently possessed by the fiber, is not sufficiently utilized in the resulting twisted cord.